Carburetor for automotive engines with a metering suction partly derived from a laminar air flow matrix

ABSTRACT

The carburetor produces increased fuel-air ratio towards the reduced airflow end of the family of constant-throttle variableR.P.M. curves (FIG. 7 curves i j k). This is obtained by augmentation of the Venturi suction by means of a Laminar Flow Matrix, which produces a nearly linear relationship between airflow and metering suction. In order to maintain the correct roadload curve despite this low-end increase of the metering signal, a bypass throttle, controlled by the main throttle, resets the fuel-air ratio to the correct value (FIG. 6). The schedule of bypass throttle opening relative to main throttle opening determines the roadload curve.

United States Patent [191 Morgenroth CARBURETOR FOR AUTOMOTIVE ENGINES WITH A METERING SUCTION PARTLY DERIVED FROM A LAMINAR AIR FLOW MATRIX [76] Inventor: Henri Morgenroth, 3090 Hidden Valley Lane, Santa Barbara, Calif. 93103 [22] Filed: July 1, 1968 [21] Appl. No.: 741,572

[52] U.S. Cl ..261/23 A, 261/56, 261/51, 261/64 R, 261/64 C, 261/121 A, 26l/DIG.

63, 261/72 R, 261/DIG. 67

[51] Int. Cl ..F02m 7/04 [58] Field of Search ..261/42, 63, 64, 23.1, 261/64.4, 51, 56, 121 A, DIG. 63, 72 R,

DIG. 67, DIG. 48

[4 1 May 1,1973

FOREIGN PATENTS OR APPLICATIONS 677,658 l2/l929 France ..261/64 366,522 2/1932 Great Britain. ..261/52 889,982 2/1962 Great Britain ..261/72 OTHER PUBLICATIONS Combustion, Charles H. Fisher, Volume 2, TJ n87, F5, 1952, Chapman & Hall, Ltd. 3rd edition London, England, pages 23 to 27 and 36 to 42.

Primary Examiner-Tim R. Miles Att0rneyLon H. Romanski [5 7 ABSTRACT suction by means of a Laminar Flow Matrix, which [56] References Cited produces a nearly linear relationship between airflow UNITED STATES PATENTS and metering suction. In order to maintain the correct roadload curve despite this low-end increase of the 2,025,862 ig/igg's aeitgen 321721;: metering Signal a bypass throttle, controlled by the 9x93] [63 X main throttle, resets the fuel-airratio to the correct 10/1933 Mock 6t 261/64 x value (FIG. 6). The schedule of bypass throttle open- 2,638,330 5/ 1953 Morgenroth ..261/23 A ing relative to main throttle opening determines the 2,779,576 l/l957 Morgenroth ..261/64 C roadload curve. 2,791,990 5/1957 Grieb 26I/DIG. 48 w 7. 7. 7 3,432,152 3/ 1969 Sweeney ..261/51 X 25 Claims, 37 Drawing Figures SECONDARY PRIMARY STAGE Z/ STAGE PAIEIIIEIIIIII' H V 3,730,495

SHEET 1 UF 8 FUEL/AIR RATIO 4 ROAD LOAD I THROTTLE CURVE p70 065" 3OW$IOTTLE 065 .060 I c Y I 060 I 11 .6 TRANsIENT cuRvEs I I4. I); I; II 050 I 00 AIRFLOW OEM. I5 50 I00 OEM.

CONVENTIONAL CARBURETOR cONvENTIONAL AIR vALvE cARsuRETOR k g- FuEL AIR Z RATIO O TRANSIENT CURVES .070-

' 11, LAMINAR FLOW ROAO LOAD MATRIx vENTURI 062 & MATRIX I III .060 I060 .o57---- O55- I5, v D55. 1,. VENTURI 050 M ETHROTTUEZL A E 2(5 50 I00 OEM. NEW EARBURETOR I MIXTURE CURVES RESULTING FROM j SUCTION CURVES OF FIG.4

INCH H III 9 4 vENTuRI a 'ESEEEJQ 11 LAMINAR FLOW MATRIX CARE 3 MAT Ix CARE.

111 vENTuRI &

MATRIx CARB.

' I I vENTuRI CARB.

25 5o I00- METERING sucTION OEM cuRvEs 11 LAMINAR FLOW IVENTUR CARB. MATRIx CARB.

.ZZ g5 PATENTEDWWHE175 3,730,496

I I snmaur's SECONDARY STAGE FUEL/AIR RATIO ROADLOAD CURVE TRANSIENT- CURVE 5 I5 25 50 200 250 yr 1: n: V

l i/MAE) SE CO/VOA Z V I PATENTEDW 1127a SHEET l} 0F v Rl MARY CARB. 5 ROADLOAD CURVE NATURAL MIXTURE CURVE OF FIG. l8 CARB. WITH AIR VALVE OPEN l'oo PATENTEU rm "1 1975 SHEET 6 [1F 8 PAUZNTED HAY 1 I973 sum 7 or a FUEL/AIR RATIO FIG. 26! A v FIG. 25 .060 j? a FIG. 26a .050

FUEL AIR RATIO CURVES GENERATED BY FIG. 27 6O 80 cm. METERING SUCTION CURVES 2O .40 METERING SUCTION CURVES 2617 Z02 ZU/ w; f/5 20% g v2/5 CARBUIRETOR FOR AUTOMOTIVE ENGINES WITH A METERING SUCTION PARTLY DERIVED FROM A LAMINAR AIR FLOW MATRIX BACKGROUND OF THE INVENTION The invention relates to automotive carburetors which are calibrated to a lean mixture, in order to reduce both harmful emission products and fuel consumption.

Since the fuel-air ratio of convention carburetors leans out at reduced airflow, the leanest possible calibration is limited by this tendency to further reduce the mixture strength at low loads.

Prior art carburetors have avoided this low-end leaning out by means of airvalves. These are devices which increase the metering suction by means of air throttling (choking) ahead of the fuel discharge. Typically, these airvalves are operated by suction sensitive devices, which tend to CLOSE these airvalves as the airflow is REDUCED. It is possible to produce flat fuel-air ratio curves with these known devices, or even curves which are getting richer towards the low airflow end.

Automotive engines equipped with such air valve carburetors, (or equivalent compensating devices) and calibrated to a very lean flat fuel-air ratio curve over the cruising range, preforms well for all throttle positions, but only in steady state operation, that is only for the constant vehicle speed obtained for each throttle position.

However, if the throttle-opening is increased suddenly, these carburetors suffer from lagging and hesitation during the acceleration which follows an increase in throttle-opening, when calibrated to a lean roadload curve. A temporarily enriched mixture would be required, in order to allow the engine to speed up to the new powerlevel and R.P.M. belonging to the larger throttle opening.

It would be easy enough to calibrate the airvalve operating mechanism in such a manner that it produces sufficently strong mixture enriching at low airflows, in order to achieve good transient response. However, this OVER compensation is not practical, since it would also produce a rich fuel-air ratio at low-load steady-speed operation, as will be more fully explained later. I

FIG. 1 shows a typical roadload curve for a CON- VENTIONAL carburetor (without airvalve). The fuelair ratio is plotted against the airflow, and each point of this curve is measured at the constant engine and vehicle speed obtained on a level road, for different throttle openings.

The curves 11,11 and c, represent constant-throttle varaible-R.P.M. Transient curves. Curve b, for instance, occurs when the throttle opening is suddenly increased from, for instance, at point I to the 35 position, and then held steadily in this 35 position. The vehicle will now accelerate from m/h ALONG THE CURVE b, increasing the R.P.M. until the airflow of 50 CFM at the intersection of curve b with the roadload curve is reached at 60 m/h.

The fuel-air ratio shown by the transient curves a b and c of a conventional carburetor tend to lean out at low R.P.M. and airflows. Consequently, when the throttle was suddenly opened from its 10 position at point I, to 35, the fuel-air ratio dropped of to point II. This is the cause of the engine hesitation and sudden powerloss in transient driving conditions.

FIG. 2 shows the same constant-throttle, variable- R.P.M. curves d and e, if they are corrected by the prior art airvalves. With the aid of the airwalve, these curves are now sloped in the desired direction of enrichment towards low airflow, thus preventing hesitation in transients.

However, as FIG. 2 shows, the roadload curve itself will, through the effect of the same airvalve, also get richer for smaller throttle positions, thus ruining the objective of low fuel consumption and emission numbers at small loads in steady speed driving.

In other words: The enriching done at low airflows by means of the prior art airvalves is simply limited by fuel-air ratio calibration requirements at low airflows,

as expressed in the desired roadload fuel-air ratio curve. If the transient curves are properly corrected, an undesirable OVER-correction of the roadload curve also results.

There exists two opposing requirements: For low airflow steady-speed operation, along the roadload curve, a LEAN fuel-air ratio is required. On the other hand, for transients, during the acceleration along the constant-throttle variable-R.P.M. curves, a RICH mixture at the low end of these curves is required.

The desired and ideal shape of fuel-air ratio curves, which fulfills these OPPOSING requirements is shown in FIG. 3. Here, the transient curve f,g,h are getting richer towards small airflows, whereas the roadload curve stays fiat, at a constant lean fuel-air ratio, over the entire cruising range. This chart illustrates the basic diffuculty in fulfilling the just mentioned theoretically best fuel-air ratio prescription, namely, that the SAME airflow, of for instance 25 C.F.M., should produce a fuel-air ratio of 0.057 in the 15 throttle position on the roadload curve, (that is for steady vehicle speed), but should also produce a richer fuel-air ratio of 0.062 if this same 25 C.F.M. airflow is traversed with a throttle position of 35, during an acceleration along curve g.

The invention gives novel means which, for the first time, achieve these two contradictory requirements. This is done by two mechanism or means acting IN COMBINATION: The first is the known airvalve or the, for this purpose newly used, Laminar Flow Matrix, which bends the constant throttle variable R.P.M. curves f g h into the desired backwards slope shown in FIG. 3. The second mechanism is a variable air-bypass system, which is coupled to the throttle and which resets the roadload-fuel air ratio curve to the desired lean values at low loads. (FIG. 6)

Thus, the invention makes it possible to calibrate the carburetor to an extremely lean roadload curve, and yet preserve good transient response (acceleration) during sudden change from any chosen .throttle position to any other chosen throttle position. In tests with this new carburetor, this automatic changing of the fuel-air ratio from transient rich to roadload lean has proven to do away with the acceleration pump, and furthermore provides an entirely new freedom to calibrate the carburetor to the most favorable lean roadload curve, without being compromised by the formely resulting poor transient response, which would occur in a conventional carburetor, calibrated to the same lean values.

SUMMARY OF THE INVENTION This invention relates generally to carburetors for internal combustion engines and pertains more particularly to emission surpressing carburetors as used on automotive engines. These carburetors are operating with the relatively lean fuel-air ratios which give the lowest percentage of underisable emission products. The carburetor according to the invention produces a set of new metering curves (FIG. 3) which permit to operate an internal combustion engine with lean mixture calibration (down to 0.053 fuel-air-ratio) along the roadload curve and yet avoids the hesitation and lagging occuring with conventional lean carbureted engines upon increasing the throttle openings, that is in transient operation (curves f, g and h). The invention consists of means to realize these new metering curves.

In the simplest embodyment of the invention, the new carburetor employs a laminar flow matrix arranged ahead of the Venturi (FIG. 6, primary stage carburetor on right side shows the invention).

The Venturi 3 produces a metering suction acting on the fuel discharge orifice 1, which rises (approximately) with the square of the airflow (see FIG. 4 curve 1). The Laminar Flow Matrix gives a linear relation between metering suction and airflow. (FIG. 4 curve II). If both a Venturi and a Laminar Flow Matrix are combined, a suction curve of intermediate curvature of the metering suction, plotted against airflow, is produced. (FIG. 4 curve I").

The fuel-air ratio curve generated by the metering suction curve according to FIG. 4 III, that is by means of a Laminar Flow Matrix and a Venturi combined, becomes richer at part throttle operation (FIG. 5, curve lllr). As explained in the chapter Background, this is desirable for the family of constant-throttle variable-R.P.M. curves, but undesirable for the roadload curve.

According to the invention (FIG. 6), the roadload curve of a carburetor with a Laminar Flow Matrix (6) and a Venturi 3 is reset into the required correct shape by means of a bypass throttle 8 which is driven by a cam 12 (or other scheduling means) attached to the throttle shaft 4. The opening sequence of this airvalve is scheduled to reduce the metering suction which acts on the fuel orifice 2 to the required amount, at each point of the roadload curve, as shown in the pictures of the throttle opening sequence of FIG. 7. Thus, the cam shape connecting the two throttles can be selected to produce the most desirable roadload curve.

The interconnection between the main throttle and the bypass throttle is purely mechanical (and NOT manifold suction operated, as in many known air valve carburetors). Consequently, the bypass throttle resets the fuel-air ratio strength only when the main throttle opening is changed; it corrects the roadload curve from the shape of FIG. III to the desired shape of FIG. 7. For constant throttle position airflow changes however, (curves i,i,k, FIG. 7) the mechanical connection causes the bypass throttle to remain in a constant position. Thus, the family of constant-throttle variable-R.P.M. curves becomes enriched at the lower air-flow end, under the influence of the matrix.

The following example will illustrate how this affects transient throttle conditions (FIG. 7). When operating the car with throttle opening at a steady 20 m/h, the

carburetor produces an 0.057 fuel-air ratio with an airflow of 15 C.F.M. When the throttle is now SUD- DENLY opened to the 35 position, the airflow grows to 25 C.F.M., according to the increased throttle opening, with still the same 20 m/h. The carburetor operation has now been shifted to point II of the low end of the 35 constant-throttle variabIe-R.P.M. curve j. The new 25 C.F.M. airflow intersects this curve at the fuelair ratio 0.062. Consequently, with the sudden throttle movement from 10 to 35, the fuel-air ratio snaps up from 0.057 to 0.062 (without the help of conventional crutches, as acceleration pumps or powervalves).

The increased throttle opening now produces an acceleration of the vehicle, along the 35 constant throttle curve j, until the steady state condition at the airflow of 50 C.F.M. is reached at the intersection with the roadload curve. Here, the carburetor has returned to produce the economical 0.057 fuel-air ratio, so that in the following steady speed driving the engine again works with favorable low emission ratio.

From the foregoing explanation it is apparent that, despite the powerless inherent in the calibration to a very lean cruising fuel-air ratio for steady speed driving, acceleration without hesitation still takes place when the throttle opening is increased, because every positive throttle opening change immediately shifts the carburetor metering up to a best power producing richer mixture at a low airflow point of the new setting to a higher constant throttle position curve. As the engine subsequently accelerates, it returns to the lean roadload curve.

The relative dimensioning and the distribution of the metering suction between the Laminar Flow Matrix (FIG. 6 Part 6) and the Venturi 3 determines the slope of the constant-throttle variable-R.P.M. curves. For instance, a short, small pressure drop producing Laminar Flow Matrix can be combined with a Venturi possessing a narrow throat. Some engines may even require completely flat metering curves. Then, the pressure drop of the Laminar Flow Matrix is reduced to a small fraction of the Venturi suction, and is used only to correct the tendency of pure Venturi meteringto grow leaner at low airflows.

The selection of the mechanical scheduling between the main throttle and the bypass throttle, (that is the shape of the cam 12), determines the shape of the roadload curve.

In carburetors with conventional correction means, such as airvalves, a change in the slope of the constant throttle variable-R.P.M. curves is always resulting in an equivalent change of the slopes of the roadload curve. The new system permits for the first time to calibrate BOTH kinds of metering curves separately, to the best shape demanded by the engine. Present demands of a flat lean cruising power roadload curve can be combined with constant-throttle variable-R.P.M. curves, which exibit a slope giving richer ratios at low R.P.M.

BRIEF'DESCRIPTION OF DRAWINGS FIG. I shows conventional metering curves.

FIG. 2 shows the metering curves of a conventional carburetor with an airvalve.

FIG. 3 shows the metering curves which are the aim of the invention.

FIG. 4 shows three basic metering suction creating devices and their suction curves (venturi, laminar flow matrix an a combination of both).

FIGS. 4-A, 4-8 and 4-C respectively, in fragmentary diagrammatic form, illustrate the three types of carburetors employed in developing the curves of FIG. 4.

FIG. 5 shows the fuel-air ratio curves obtained with the devices of FIG. 4.

FIG. 6 shows one schematic section of one form of execution of the invention, containing the basic components of invention.

FIG. 7 shows the metering curves obtained with the carburetor of FIG. 6 and shows furthermore different throttle positions of the carburetor of FIG. 6, for different airflows.

FIGS. 7A, 7B, 7-C, 7D, 7E and 7F respectively, in diagrammatic form, illustrate the carburetor structure of FIG. 6 in varying operating positions corresponding to indicated areas of operation depicted in FIG. 7.

FIGS. 8A, 8-B and 8-C illustrate a modification of the carburetor of FIG. 6, in three different throttle positions.

FIGS. 9, ll, 12, 13 and 14 show schematically various devices designed to substitute the laminar flow matrix. (FIG. gives comparative suction curves for a laminar flow matrix and its substitute.)

FIG. l4-A is a cross-sectional view taken generally on the plane of line AA of FIG. 14 and looking in the direction of the arrows.

FIG. 15 fragmentarily illustrates a carburetor embodying the teachings of the invention with a reset device controlling the position of an air bypass throttle.

FIG. 16 somewhat in schematic form illustrates a carburetor constructed in accordance with the teachings of the invention wherein air bleed means is employed generally upstream of the induction passage throttle valve means.

FIG. 17-A illustrates in simplified form, a carburetor in which air bleed means, functionally equivalent to that of FIG. 16 is controlled by a plate-type valving member.

FIG. 17-B is a simplified view taken generally on the plane of line B-B of FIG. l7-A and looking in the direction of the arrows.

FIG. 18 is a graph of the fuel-air ratio curves obtained by the carburetor of FIGS. 18-A, l8-B and 18-C.

FIGS. 18A, 18B and l8-C respectively illustrate a carburetor employing an air valve for performing the reset function of the invention with such air valve being illustrated in three selected different operating positions.

FIG. l9-A illustrates a carburetor employing a reset mechanism comprising a profiled shutter for at times partially restricting flow through the associated laminar flow matrix.

FIG. 19-8 is a view taken generally on the plane of line B-B of FIG. 19-A and looking in the direction of the arrows.

FIG. 20-A illustrates a carburetor employing a variable venturi as the reset means of the invention.

FIG. 20-B is a view taken generally on the plane of line B-B of FIG. 20-A and looking in the direction of the arrows.

FIG. 20-C is a view similar to FIG. 20-B but illustrating the elements thereof in an operating position different from that of FIG. 20-B.

FIG. 21 illustrates, in cross-section, a carburetor employing a variable area fuel discharge orifice as cornprising the reset means of the invention.

FIG. 22 to 33-A shows the new carburetor with different shunts of the laminar flow matrix and the ventu- FIG. 34 and 35 shows a method to reduce the size of the matrix.

. FIG. 36 shows a two-stage application of FIG. 35.

DETAILED DESCRIPTION Table of Content 1. Terminology, as used in description and claims.

2. Purpose of new carburetor: New metering curves and their advantages.

3. The basic combination of a laminar flow matrix and a reset mechanism which accomplishes these new metering curves. One form of execution (FIG. 6).

4. Idle.

5. Cooperation of new first stage carburetor with second stage carburetor.

6. Means and .methods for shaping the metering curves with different laminar flow matrix-venturi combinations: a.'Roadload curve b..Transient curves, selection of slant angle.

' c. Selection of laminar flow matrix.

d. Variation of slant angle between members of the family of transient curves.

7. Devices simulating the laminar flow matrix.

(Matrix substitude).

8. Selection of best metering suction producing device. (Best laminar flow matrix or matrix substitute-venturi combination).

9.- Summary of requirements for metering suction producing devices.

10. Seven reset devices:

a. Bypass throttle (FIG. 6).

b. Interior discharge throttle (FIG. 15). c. Bleed air valve (FIG. 16 and 17).

d. Airvalve (FIG. 18).

e. Variable matrix area (FIG. 19).

f. Variable venturi (FIG. 20).

g. Variable fuel orifice (FIG. 21).

1 1. Different shunts of the venturi, the laminar flow matrix or its substitute, for accomplishing the transient curves which grow richer with reduced airflow.

a. Matrix (or substitute) and venturi in series (FIG.

b. Matrix (or substitute) and venturi in parallel (FIG. 22, 23 and 24).

c. Matrix in airbleed passage (FIG. 25).

d. Matrix controls float bowl vent (FIG. 29 & 33).

I2. Matrix controls excessively rich carburetor, with air-dilution by means of interior discharge throttle (FIG. 34, 35 & 36). 13. Conclusion.

l. TERMINOLOGY, AS USED IN DESCRIPTION AND CLAIMS Wherever terms conforming to the following explanation are INTRODUCED into the description, these terms are capitalized.

In the claims, these terms are capitalized throughout.

1. New Carburetor I The fuel and air metering system according to the invention.

2. Steady State condition or operation This is the operation at the engine R.P.M. and mixture flow which occurs for each throttle position, in level, constant speed driving. For each throttle there exists a speed in level driving where the total of all moving resistances are exactly balanced by the engine torque delivered at this particular throttle opening and engine R.P.M.. Here all acceleration or deceleration disappear and the vehicle assumes a constant level speed.

3. Roadload curve or Steady State curve (FIG. 1)

A curve plotting fuel-air ratio against mass airflow, as it occurs over the full range from idle R.P.M. with a relatively rich mixture, over LEAN CRUISING, up to full power R.P.M. at wide open throttle with a rich, best power mixture. Going up this curve from idle, BOTH the throttle opening and the engine R.P.M. are increased for each subsequent point. Each point of this Roadload Curve represents one Steady State operating condition.

4. Transient operating condition An accelerating or decelerating condition which results from leaving the roadload curve through a SUD- DEN change of throttle position. See for instance the lines connecting points I, II, III in FIG. 1. The car has operated at the steady speed of 20 m/h, with 10 throttle opening, at point I. Then the throttle was SUD- DENLY opened to the 35 position, thus disturbing the m/h Steady State and momentarily arriving at the airflow and mixture ratio corresponding to point II. Now, an acceleration with the new constant 35 throttle opening takes place along the curve b. Until this acceleration leads to the next Steady State point III at 60 m/h, a Transient operating condition prevails.

5. Transient curves or Constant Throttle-Variable R.P.M. (or Variable Airflow) curves These are the family of curves (FIG. 1 a, b and c) which plot fuel-air ratio change against airflow change during the just described Constant-Throttle Transient conditions. (In common usage, transient may describe also other changing conditions. In this description, Transient. curve is used only in the narrower meaning given above).

6. Lean mixture A fuel-air ratio which sustains running of an internal combustion engine with some LOSS in torque, but which is NOT yet leaned out to an amount where uneven firing and missing occurs. It is also a mixture strength which gives the mimimum of undesirable emission products. With present designs of combustion chamber, such a Lean mixture occurs at fuel-air ratio between 0.0560.058. The number 0.057 arbitarily designates in this description this mixture strength. With progress in the art of design of combustion chambers, ignition and stratified charge devices, this particu lar value may change.

7. Rich mixture A mixture strength which gives best power, by buying this power increase with higher specific fuel consumption and higher percentage of emission products. Arbritrarily, this Rich mixture is chosen here to extend from 0.062 to 0.070.

8. Excessively Rich mixture A mixture, usually of a fuel-air ratio above 0.20, which is too rich'to operate an engine, and which has to be diluted with a separately controlled air addition to provide the correct Roadload mixture curve.

9. Two Stage carburetor, Primary carburetor, Secondary carburetor Essentially two carburetors, (usually with common Fuel Level Holding device). The Primary carburetor serves the lower range, from idle to an intermediate power level. This Primary carburetor serves all but the highest power levels of cruising speeds, and is also sufficient for moderate acceleration. This is the carburetor which is calibrated Lean, for lowest emission numbers and best fuel economy, rather than best power.

' The Secondary carburetor joins the Primary carburetor unfrequent use of the Second stage, its greater production of emission products and higher fuel consumption can be tolerated.

10. Fuel Level Holding mechanism or device The Fuel Level Holding mechanism establishes the exact pressure or level of the fuel before it enters the fuel metering orifice. It may consist of a conventional float mechanism, or a fuel spilldam, or a diaphragm operated valve.

l l. Vent for the Fuel Level Holding mechanism This is the airconnection to the airspace above the floatlevel of the floatbowl, or to the airspace above the spilldam level, or to the dry side of the regulating diaphragm. It establishes the pressure before the fuel metering orifice (together with the hydrostatic head).

12. Main Passage The passage which receives combustion air, (usually from an airfilter) and receives fuel from one or several fuel metering orifices, either as solid fuel or, if

premixed with bleed air, as a foam. The Main Passage discharges the fuel-air mixture into the engine manifold.

13. Main Throttle The throttle valve which determines the amount of fuel-air mixture flow to the engine, and which is usually connected to the footpedal (or a governor). The Mai Throttle is located in the Main Passage.

l4. Bypass Throttle A valved air passage which reduces the metering signal by means of admitting air bypassing the Venturi and/or Matrix or Matrix substitute. (FIG. 6, throttle 8 and FIG. 8).

15. Interior Discharge Throttle A valved air passage which reduces the fuel-air ratio by admitting additional air downstream of the Main Throttle, directly into the manifold vacuum. (FIG. 15, throttle 91 & FIG. 34, throttle 245).

l6. Bleed Chamber (See FIG. 16)

The Bleed Chamber 101 forms a connection orpassage between the fuel metering orifice and the discharge port 103 into the Venturi 102. In this chamber, the metered fuel is mixed with Bleed Air.

17. Bleed Air Passage with Bleed Air Orifice (See FIG. 16)

An air passage 108 connecting the Bleed Chamber 101 with an air inlet 104. The Bleed Air Orifice 109 intersects this passage and reduces the Metering Suction according to its flow area.

18. Bleed Air Valve (See FIG. 16)

A valve 105 controlling the flow area of the Bleed Air Orifice 109.

19. Venturi and Air Orifice Devices which produce nearly square-law relation between air-speed and metering suction.

20. Laminar Flow Matrix or the abbreviation Matrix A device consisting of a great number of parallel, long and narrow airchannels, which produces a pressure drop by means of airfriction on large surfaces (rather than by means of turbulent fiow through orifices). This device establishes a nearly linear relationship between pressuredrop through the Matrix and airspeed, at conditions below the critical Reynold number. In the New carburetor, the Matrix is also used close to the critical Reynold number for Mixed Turbulent and Laminar flow conditions.

21. Airvalve A valved, variable air passage, intersecting the main airstream and located ahead of the Venturi. This Airvalve causes a nearly square-law metering signal curve, of a different magnitude for each Airvalve position. This metering signal AUGMENTS the metering signal produced by the Venturi. (FIG. 18, valve 120).

22. Airvalve, Simulating the Laminar Flow Matrix or the abbreviation Matrix Substitute An Airvalve as defined in 21, except that it is controlled by devices opening it with increasing airflow, in such a manner that it creates a pressure-drop-airflow. relation/3p=C.F.M. (FIG. 11 & 12

23. Metering Pressure Drop Ap If the pressure at the inlet of the metering orifice is kept constant this pressure drop is simply called Metering Suction:

The pressure-drop Ap of the air passing through a suction generating device (for instance a Venturi), this pressure drop causing and controlling the fuel flow through a metering orifice.

This pressure-drop or suction will cause the fuel flow through the metering orifice in one of four ways:

1. The suction acts directly on the exit of the fuel metering orifice.

2. The suction is first degraded by means of an airbleed, before acting on the metering orifice. See FIG. 25. The Metering Suction is here the suction prevailing in the Bleed Chamber 183.

3. The suction acts on a diaphragm-valve combination, or other suction multiplying devices, as known from injection carburetors, this suction being converted into pressure, acting on the inlet side of the fuel metering orifice.

4. Suction acts on the inlet side of the fuel metering orifice, for instance by controlling (directly or indirectly) the pressure in the airspace above the fuel level of a float bowl. (FIG. 29) This suction is always combined with a stronger suction on the exit of the fuel metering orifice, in order to create a Metering Pressure Drop.

24. Metering Pressure Drop Producing Devices or Means The Devices or Means which cause and control this Metering Pressure Drop Ap.

These may be one of six devices, or mostly a combination thereof.

1. a Venturi 2. an Air orifice 3. a Bleed Chamber (FIG. 25, 183) 4. a bypass passage with connection to the vent (FIG.

5. a Laminar Flow Matrix 6. a Matrix Substitute 25. Reset mechanism or device and its Schedule A device causing a Scheduled changing or Resetting of the mixture strength. This schedule is determined by the angle of the Main Throttle position.

The example of FIG. 6 explains one form of execution: The Main Throttle shaft 4 carries a cam 12 which engages a roller 11, attached to lever 10. Lever 10 operates the Bypass Throttle 8, which bypasses air around the Venturi 3 and/or the Laminar Flow Matrix 6. Thus, the shape of the cam determines or Schedules the amount of bypassed air, in dependance of the Main throttle opening position. The magnitude of the fuel-air ratio reduction, caused by this bypass air, depends on the cam shape and therewith on Main Throttle positions.

Generally, a Reset Device incorporates means to change the fuel-air ratio, either by changing the Metering Pressure Drop, or by diluting the mixture downstream of the fuel discharge, or by using a variable area fuel metering orifice. The Reset Device furthermore incorporates suitable coupling devices between the just mentioned means to change the fuel-air ratio and the Main Throttle. These coupling devices are designed to have the capability to be calibrated to a schedule necessary to achieve the desired fuel-air ratio for each Main Throttle position. Expressed differently, the coupling device between the means to reset the fuel-air ratio and the Main Throttle contains mechanism, (such as cams) which can be calibrated or shaped to coordinate one desired mixture strength value to each and every Main Throttle position.

26. Calibrate and again Schedule Calibrate means giving the carburetor elements, which determine the mixture ratio, a size which produces the desired fuel-air ratio value.

These elements are the fuel metering orifice, the airflow controlling devices and the Metering Pressure Drop Producing Devices.

Furthermore, in the case of the Reset mechanism, calibrate means to assign a fuel-air ratio of its own to EACH Main throttle position, for instance by shaping the cam 12 so as to produce the desired magnitude of the fuel-air ratio correction for each cam position, and therewith for each Main throttle position. Thus, the cam represents in this example the Scheduling means which is Calibrated to produce individually desired fuel-air ratio values for each Main throttle position.

27. C. F. M.

C.F.M. refers here to the Cubic Feet per Minute of combustion air passing through the carburetor to the manifold. When this term is used in an equation, corrective factors for density and constant factors for dimensions are, for simplicity sake, left out of the equation as irrelevant for the understanding of the invention.

2. PURPOSE OF NEW CARBURETOR: NEW METERING CURVES AND THEIR ADVANTAGES FIG. 1 shows a Steady State Roadload fuel-air ratio curve, with Lean calibration over the cruising range. The additional curves a b and c are the Transient Constant-Throttle variable R.P.M. curves for conventional carburetors (See Terminology 25) These Transient curves are somewhat leaning out, towards their low airflow end, (or at best maintain a constant fuel-air ratio over some length of the operating range).

The limitation for the leanest possible calibration is imposed by this low end leaning out. For STEADY STATE operation, along the roadload curve alone, it would be acceptable to lower the mixture ratio for cruising considerably under presently used values. However, with such a very lean mixture, lagging and even missing would then occur in TRANSIENT conditions, since transients demand a richer mixture than the steady state condition.

The New carburetor produces a family of constantthrottle variable-R.P.M. curves as shown atfg and h in FIG. 3, which becomes RICHER at LOW airflows and R.P.Ms. Tests have shown that the constant fuel-air ratio cruising power region of its roadload curve can be lowered to 0.053, and still transient operation without loss in drivability be maintained, even without an acceleration pump. In contrast with this, with a conventional carburetor and the same engine, the cruising mixture had to be increased to 0.059 or 0.060 to give comparable transient performance.

The reason for this superiorty of the new carburetor is that, whenever steady state driving is interupted by sudden opening of the main throttle to any greater opening position, the new carburetor with the backwards sloping family of curves fg & h at once shifts to operation with increased fuel-air ratio.

FIG. 7 shows the backward slanting transient curves i i j & k of the new carburetor in more detail. The accelerating example is here repeated with the line l-ll- Ill. The car had been operated with 20 m/h and 10 throttle with the steady state airflow of C.F.M. and an 0.057 fuel-air ratio. Now the throttle is suddenly opened to 35, and after this movement held steadily in this new position. The mixture flow will, during the sudden throttle opening motion, snap up along the line [-1], to an airflow, of 25 C.F.M., which results from the sudden throttle opening increase WITHOUT R.P.M. change. Therewith, the new airflow of 25 C.F.M. is now combined with the 35 opening, and the mixture ratio increases from 0.057 to 0.062 on the low R.P.M. end of the 35 constant throttle curve j. This 0.062 ratio provides maximum torque for the now ensuing acceleration. Now (while the throttle is kept steady at 35), the car accelerates along curve j, until the 60 m/h steady state point I with the airflow of 50 C.F.M. and the economical roadload value of 0.057 ratio for constant speed driving has been reached again.

Thus, while accelerating along curve j, the engine is gradually shifted from a best-torque rich ratio to the best-emission lean ratio which occurs at the intersection with the roadload curve. Shortly before reaching point III the engine enters into the region of torque loss, caused by mixture leaning. This creates a built-in selfgoverning feature which actually prevents the engine from overspeeding into a very lean ratio where uncarburetor flange.

tolerable torque loss prevails. Consequently, even on a slight downhill grade, the engine tends to assume the R.P.M. which gives the best operating level, along the constant-throttle variable-R.P.M. curves.

During deceleration, the engine will operate on the family of transient curves below the roadload curve, thus leaning out to below 0.057. For the sake of emission reduction, this is a desirable feature.

From this it becomes apparent that this novel separation of the roadload curve with lean mixture values on the one hand and of richer transient mixture values on the other hand, brings very greatbenefits in drivability with a carburetor calibrated to a lean roadload curve.

As explained later, the new carburetor permits to select freely the steepness of the backwards slope of the curves ij k; if desired, a very slight increase in the fuelair ratio for reduced airflows can be selected. Also, completely flat curves, with constant fuel-air ratio can 'be produced. In this case, the new system serves only to compensate for the disadvantage of conventional pure Venturi carburetors to lean out at low speeds.

3. THE BASIC COMBINATION OF A LAMINAR FLOW MATRIX AND A RESET MECHANISM WHICH ACCOMPLISHES THESE NEW METERING CURVES ONE FORM OF EXECUTION (FIG. 6)

FIG. 6 shows a simple form of the New carburetor, which accomplishes this desirable separation of the two kinds of metering curves. The drawing shows a Two- Stage carburetor. In this form of execution, only the First stage or Primary carburetor, shown on the right side, is of the design according to the invention, (although the Secondary Stage carburetor can also be designed according to the invention).

The FIRST MAIN element in the New carburetor is a Laminar Flow Matrix, producing a suction which increases in generally linear relation with the airflow, (or other devices of similar pressure drop-airflow relation).

This Matrix 6 receives air' from an airfilter (not shown). The matrix is arranged ahead of aVenturi 3. The fuel metering orifice 1 discharges into the venturi and is subjected to the Metering Suction composed by the superimposed suctions of the matrix plus the venturi. The resulting mixture passes the Main throttle 5 and is delivered to the engine manifold (not shown) at the The metering orifice 1 receives the fuel through a duct 2 from the Fuel Level Holding Mechanism. In the example shown here, it consists of a floatbowl 15, a float 16 which is hinged at the pivot 17 and which operates the fuel inlet valve 18. The Vent 19 connects the airspace above the fuel level with the inlet air of the matrix 6.

The flow resistance of the matrix decreases with reduced airflows LESS than that of a venturi, thus generating a metering suction which does NOT drop off at low airflows as much as that generated by a venturi. Consequently the carburetor, as just described, delivers a mixture which grows richer with reduced main throttle openings. (The effect of the matrix could be compared to that of a choke which is progressively closed as the airflow decreases).

This low speed rich deviation of the desired roadload curve is corrected by means of the main throttle controlled Reset Mechanism. In the example shown in FIG. 6 this reset device consists of a bypass throttle 8 which moves in an ambient air inlet 7 and which discharges air into the annular plenum space 14, which in turn discharges into the carburetor main passage at the venturi exit. For each opening angle of the bypass throttle 8 the mixture arriving from the venturi is diluted. Thus, with the proper opening sequence of the bypass throttle, the mixture curve can be reset to the desired roadload curve.

This required proper opening sequence is generated by the shape of the face of the cam 12, which is connected to the shaft 4 of the main throttle 5. The bypass throttle 8 swings with a shaft 9, which carries the lever 10, which in turn carries the roller 11. A spring 13 forces this roller into contact with the cam face.

With this reset device the bypass throttle opening is controlled and scheduled by the main throttle opening position. The selection of the profile of the cam face permits a free selection of the shape of the roadload curve.

The reset mechanism can be of many different forms of execution, which are discussed in chapter 10. It constitutes the SECOND MAIN element of the new carburetor and is ALWAYS used in conjunction with the matrix (the first main element) or a Matrix Substitute.

The bypass throttle passage can be designed to discharge directly into the carburetor. However the detour of this air discharge through the annular plenum l4 improves the distribution, and the extend of the asymetry of the plenum and its ring shaped air discharge provides also means to influence the mixture distribution to the manifold.

The metering orifice l discharges solid fuel into the venturi. In order to improve atomization, an airbleed circuitery can be fitted to this discharge. The later explained FIG. 26-A gives an example ofa bleed arrangement for maximum atomization. The conventional airbleed system, which are designed to form a compensation, are not needed in the new carburetor, since the matrix fulfills all compensation tasks. The elimination of these conventional airbleeds improves throttle response considerably.

The form of execution of the invention shown in FIG. 6 carries only a single fuel metering orifice. Since one fixed orifice can not cover the entire metering range of an automotive engine, the New carburetor forms here only the Primary stage of a Two-stage carburetor. Since low emission values and low fuel-air ratios are at present of no importance for the upper power range, the Second stage can be of conventional design and is only symbolically represented in FIG. 6, by the body 20, secondary throttle 21, fuel metering orifice 22 and venturi 23.

In order to fully understand the generation of the two kinds of metering curves (discussed in Chapter 2) by means of the new carburetor, it is first necessary to explain the three metering suction curves shown in FIG. 4, which are produced by the three schematically shown carburetors I, II and III, (which do NOT posses the reset mechanism).

The diagram FIG. 4 plots three curves of metering suction against airflow (C.F.M).

Curve I is theAP= C.E.M. the Aofa purely turbulent venturi, device I.

Curve II is the AP=C.F.M. relation of metering suction created by a matrix of pure laminar flow characteristics.

Curve III finally represents the intermediate relation AP C.F.M. resulting from the device III. This is combined of a shorter matrix and larger venturi than shown in I & II, so that the COMBINED pressure drop at maximum airflow equals that of the seperate elements I and II.

FIG. 5 plots the fuel-air ratio curves Ir, IIr and IIIr against airflow, as they result from the metering suction curves and devices I, II and III of FIG. 4.

The nearly square-law metering suction curve I of FIG. 4 produces the nearly straight line fuel-air ratio curve Irof FIG. 5, which (contrary to simplified ideal assumtion of being a constant) slants slightly towards a reduced fuel-air ratio for low airflows.

The fuel-air ratio curve Ilr (FIG. 5), which results from the metering suction curve II (FIG. 4) of a pure laminar flow matrix, shows the strongest low airflow fuel-air ratio increase.

Finally, the curve IIIr (FIG. 5), produced by the combined laminar flow matrix and venturi used in the new carburetor, exhibits an enrichment at the low airflow end which is intermediate between the pure venturi curve Ir and the pure matrix curve Ilr.

Consequently, the desired low-end fuel-air ratio increase can be selected by a fitting combination of the size of the venturi and the laminar flow matrix.

Now returning to FIG. 6, we see that the primary carburetor represented there is identical to the just discussed device III of FIG. 4, EXCEPT for the bypass throttle 8 of FIG. 6. IF this bypass throttle is kept closed, the metering curve k, shown in FIG. 7 is produced, which corresponds to the curve IIIr of FIG. 5. FIG. 7 represents a more elaborate graph of the results obtained with the device of FIG. 6.

The curve k can be produced by TWO methods of changing the air-flow. The first method is to vary the airflow by changing the setting of the main throttle 5, (while the bypass throttle for the purpose of this explanation is still kept closed.) The second method is to hold the main throttle 5 in its wide open position, and change the airflow by means of engine R.P.M. change alone.

It is apparent that the SECOND method of changing the airflow by means of R.P.M. change with constant throttle position indeed produces the desired transient curve k, (as well as the other constant throttle curve i and j, for different smaller constant-throttle positions).

It is furthermore apparent that the FIRST method to vary the airflow by changing the throttle position (with the bypass valve closed), results in an utterly wrong roadload curve ofa shape also following curve k.

Without additional corrective devices (that is with the bypass throttle 8 closed), the roadload curve simply coincides with curve k; the metering suction depends on the magnitude of airflow only, and will assume the same values, regardless whether the airflow is changed by means of throttle position changes or engine R.P.M. changes.

This is where the use of the Reset device comes in, in order to separate the two kinds of metering curves, as described in Chapter 2 as the aim of the invention. The bypass throttle 8 with its scheduled cam connection to the main throttle shaft 4 fulfills this aim. Each airflow point of the uncorrected curve k is lowered to the desired mixture strength of the roadload curve, by means of a fitting opening of the bypass throttle 8.

The carburetors diagrammatically shown respectively in FIGS. 7-A, 7-B, 7C, 7-D, 7-E and 7-F are a repeat of the carburetor of FIG. 6, for six different load conditions, each corresponding to one point of the roadload curve. These figures show the relation between the openings of the two throttles.

The new carburetor system of the primary stage covers the cruising range from 5 C.F.M. at idle to I20 C.F.M., which is the airflow at the top of the economical part load operation. From 15 to 120 C.F.M., this primary stage carburetor is calibrated to a roadload curve with the most economical ratio of 0.057. Over this entire range, the secondary, conventional carburetor remains closed.

Beginning at point I of the roadload curve of FIG. 7, the main throttle of FIG. 7-B is correspondingly illustrated at the 10 position. The bypass throttle is almost completely open, since the bypass has to provide here the largest mixture correction from the corresponding airflow point of the curve k. (It is to be remembered that the laminar flow matrix WOULD produce a roadload curve similar to the transient curve k, IF the bypass throttle would not be opened).

Next, as illustrated in FIG. 7-C, the throttle is opened to the 35 position. If very gradually opened, the car just increases speed with the mixture ratio given by the roadload curve. If, on the other hand, the throttle is suddenly opened, and then kept steady at the 35 position, the mixture ratio follows (as explained previously) the points I-II-III, with an increase of the fuelair ratio to 0.062 at point II, and a gradual return to 0.057, after accelerating up to the balanced point III at the intersection with the roadload curve.

The carburetor picture of the 35 throttle position shows that the bypass throttle opening is here considerably reduced. The reason is, of course, that the needed mixture strength correction from the corresponding point of the curve k is now less that at the previous C.F.M. 10 throttle point.

Now, going further up the roadload curve, the wide open throttle position (of the new primary carburetor) isfinally reached as generally depicted in FIG. 7-D which, in turn, corresponds, for example, to an air flow, in FIG. 7, of 120 C.F.M. The-corresponding picture of FIG. 7-D shows that the bypass throttle is here completely closed. The reason is that the curve It, produced by the combined matrix and venturi generated metering suction, without bypass correction, intersects the roadload curve here.

An R.P.M. change from this open throttle position, be it during a previous acceleration, or when entering a grade, will result in fuel-air ratio changes along the curve k, since, with constantly open main throttle position the bypass remains closed.

It is apparent that the amount of correction created by the bypass throttle openings depends on the profile of the cam 12 which positions the bypass throttle. It follows that the selection of this profile permits the selection of any desired shape of a roadload curve.

This detailed explanation gives the corrective relation between main throttle opening and bypass throttle opening, which results in the lean roadload curve. It also shows the enriching effect of operation at R.P.M.s which are lower than the R.P.M.s of the corresponding roadload throttle opening; with these reduced R.P.M.s', the bypass throttle position is at the smaller opening, assigned to the higher main throttle opening. The picture FIG. 7 shows that the movement of the two throttles (the primary carburetor throttle valve and the bypass throttle valve) is essentially opposed, over the constant 0.057 mixture range.

4. IDLE Once more returning to the roadload curve, a closing of the main throttle from 10 to a 2 or 3 position as depicted in FIG. 7-A brings the carburetor delivery into the idle range. Roadload curves for this region are always calibrated to become richer, somewhat according to the shape shown in FIG. 7.

Conventional carburetors need the added fuel supply from-a separate idle system.

It is a great advantage of the new carburetor that it does not need an idle orifice, but that it can supply any degree of richness in the idle range with the main orifice alone. This is simply done by closing the bypass throttle (which was almost completely open in the previous l0 position) when the main throttle is closed to the 2 or 3 idle position. The closing schedule and the amount of closing of the bypass determines the steepness of the fuel-air ratio curve between 15 and 5 C.F.M., as well as the amount of idle enrichment.

The idle mixture adjustment is obtained by changing the bypass throttle position at idle, by means of a variable end of the cam, or an overriding mechanism A further great advantage of the elimination of the conventional idle system is the lack of the troublesome and sensitive fading-out of the idle orifice and fading-in of the main orifice, at the beginning of the cruising range. Accurate metering in this region is much more easily obtained with the single orifice system of the new carburetor.

5. COOPERATION OF NEW FIRST STAGE CARBURETOR WITH SECOND STAGE At the high airflow end of the roadload curve of FIG. 7. from C.F.M. to full power, the secondary carbu-, retor throttle opens, while the primary carburetor throttle remains in its open position as generally depicted in FIGS. 7-E and 7-F.

In conventional carburetors, the secondary stage can NOT be of the simple basic design, shown in FIG. 6, since its fuel-air ratio curve leans out at low secondary throttle openings. In order to prevent a hole in the region where the secondary opens, a great variety of compensation mechanism are employed.

Furthermore, frequently a powervalve has to be opened during the second stage operation, in order to produce the needed wide open, best power, rich operation.

The new primary carburetor in its cooperation with the secondary stage, offers the great added advantage of eliminating such crutches" for the second stage, for the following two reasons:

Firstly, when the second stage throttle opens, the mainfold suction drops and therewith the airflow through the primary, Laminar Flow stage is reduced.

This airflow reduction for the constant wide open primary throttle has the SAME effect as an airflow reduction caused by engine R.P.M. reduction; the primary carburetor reduces its delivery according to curve k, and consequently its fuel-air ratio increases. Thus, this increase can make up for the drop in fuel-air ratio caused by the low flow delivery of the conventional secondary stage.

Second, the reset mechanism can also be used to correct the part throttle leaning out of the secondary stage. Furthermore, this primary reset mechanism replaces the conventional power valve. The sequence of throttle positions for 120 C.F.M, 170 C.F.M. and 240 C.F.M. of FIG. 7, and as correspondingly depicted in FIGS. 7-D, 7-E and 7F, explains these compensations.

At 120 C.F.M., the top of the primary range, the bypass throttle is completely closed.

At 240 C.F.M., the wide open position, the bypass throttle is also closed. In order to obtain an 0.070 rich fuel-air ratio, without the help ofa powerjet, an accordingly large fuel orifice (22 in FIG. 6) is employed.

Going now down to the I70 C.F.M. position, the wide open 0.070 ratio would then be undesirably high. Here, with conventional carburetors, the powervalve 7 would close off and reduce the fuel flow to, for instance, an 0.061 ratio.

With the help of the bypass throttle, this is now possible WITHOUT a powervalve. The bypass throttle 8 can be operated by means of a main throttle dependent cam, or (better) by means of a manifold vacuum sensitive diaphragm, opening it to the selected intermediate position shown in the drawing, thus reducing the ratio to the desired 0.061 level.

Going further down to the 130 C.F.M. region, where the secondary throttle is just cracked open and delivers only a very small airflow, the fuel-air ratio of the conventional secondary stage may fall off to very lean values. To avoid this, it is only necessary to schedule the reset mechanism in such a way that the bypass throttle again is returned into its closed position, thus pushing the ratio to higher values. This closed position is then maintained when going further down to 120 C.F.M., the top of the primary range, where the secondary carburetor ceases to work.

Thus, the reset mechanism of the NEW primary carburetor can be used to give to the roadload curve delivered by the secondary, CONVENTIONAL stage the best desired shape.

6. MEANS AND METHODS FOR SHAPING THE METERING CURVES WITH DIFFERENT LAMINAR FLOW MATRIX VENTURI COMBINATIONS a. ROADLOAD CURVE The dependance of the roadload curve from the cam shape makes it possible to calibrate the roadload curve of the new carburetor to almost any desired shape (See chapter 3). b. Transient Curves, Selection of Slant Angle As briefly explained before, the slant angle of the constant-throttle variable-R.P.M. curves can also be freely selected. For instance, in order to obtain a transient curve of reduced steepness, it is only necessary to select a shorter matrix of reduced pressure drop,

and then replace the pressure drop reduction with a suction increase derived from a smaller venturi. With this procedure, even almost flat transient curves can be created (where the short laminar flow matrix only corrects for the low airflow leaning-out). This may be desirable for engines operated with a great variety of R.P.M.s, such as aircraft engines, where transients are of lesser importance. Even with such flat curves, the new system is still superior to conventional carburetors, since conventional carburetors exhibit curves sloping entirely in the wrong direction (leaning out at low flows). Indeed, the basic elements of the new carburetor are all retained, even with flat constant-throttle variable-R.P.M. curves. Only the size of the Laminar Flow component and the bypass throttle passage is reduced.

0. Selection of Laminar Flow Matrix A Laminar Flow Matrix supplies a strictly linear relation between airflow and pressure drop for slow airspeeds only (produced with a large matrix area), at a Reynold number under 600. For small-area laminar elements, with higher Reynold Numbers, an exponential distortion is increasingly added, until at (or before) the Reynold number 2,000 almost purely turbulent flow prevails.

In the new carburetor the linear airflow-suction relation of the matrix is anyhow degraded, by means of the added venturi. Therefore it is not necessary to use a very large matrix with pure laminar flow. Rather, a smaller matrix, with PARTLY linear and partly turbulent characteristics, close to the Reynold number 1,500 at maximum airflow can be selected, thus taking over part of the function of the venturi. The venturi should then be chosen with an accordingly larger throat, since the matrix takes over part of its turbulent function. In some cases, the venturi can thus be eliminated altogether, and the matrix alone serves the purpose of creating an intermediate suction-airflow relation, according to curve III of FIG. 4.

In some applications, the matrix can be sufficiently small to enter an almost entirely turbulent flow area at the top of the primary range, if the roadload curve is shifted here anyhow to richer best power ratios. To summarize: A pure Laminar Flow Matrix has a relation ofAP= C.F.M..

A purely turbulent Venturi has a relation of AP C.F.M. 1

The Laminar Flow Matrix serving the new carburetor should, over the major portion of the lean part of the roadload curve, remain in the range of values AP C F M l |.9 V d. Variation of Slant Angle between Members of the Family of Transient Curves The new carburetor also offers the possibility to select transient curves of a steepness which vary for different main throttle positions. For instance, the slope of curve k in FIG. 7 can be reduced to the dashed line, by selecting a smaller matrix which has a larger turbulent component in the upper airflow region.

It is also possible to use a movable shutter in FIG. 19) which blanks off part of the matrix area, and which is moved and controlled by the main throttle. (This device is more fully explained in Chapter 10 and FIGS. 19-A and 19-B). By proper scheduling of the shutter movement, and therewith the area reduction of the matrix, any desired distribution of steepness of the slope of the family of transient curves can be obtained. Since such a reduction of the matrix area also influences the roadload curve, this influence must be compensated by scheduling the bypass throttle accordingly.

It is also possible to combine a variable venturi with a constant matrix area, and control the venturi throat area variation from the main throttle.

The use of the just described additional mechanism for influencing the slant angle distribution can be avoided by using different combinations of shunting the reset bypass channel into the main airflow. The influence of these different shunt combination will be explained in Chapter 11b, as these different devices are discussed. As an example it shall suffice here to explain the device shown in FIGS. 8-A, 8B and 8C.

This primary carburetor is identical to the primary stage shown in FIG. 6 and 7, except for the location of the discharge of the bypass airflow into the main stream. In FIG. 6 and 7 the discharge takes place BE- HIND the /venturi. In FIG. 8 the bypass throttle discharges AHEAD of the Venturi. FIGS. 8A, 8B and 8-C respectively show three opening positions for 15, 50 and 120 C.F.M. In the 120 C.F.M. position where the bypass is closed, both the devices of FIG. 7 and FIG. 8-A give obviously the same curve k. For lower airflows however, where the bypass throttle opens, a difference in the slope of the curves will result. The shunting of the carburetor (as depicted in FIGS. 8A and 8B) produces the dashed, flat angled curves m and n, (while k remains on the solid line) since a larger percentage of air traverses the square law venturi in these positions, thus diminishing the percentage of the contribution of the laminar flow matrix (which was the cause of the low-end fuel-air ratio increase). Of course the reset mechanism, (that is the shape of the cam driving the bypass throttle) has to be made to match the new conditions.

7. DEVICES SIMULATING THE LAMINAR FLOW MATRIX (MATRIX SUBSTITUTE) As explained previously, the purpose of the Laminar Flow Matrix in the new carburetor is to create a suction which rises proportional to the airflow, or provides a suction curve somewhere halfway between a linear relation'and a square relation to the airflow.

It is possible to simulate such a curve with airvalves which are opened and closed on a schedule generating a linear relation between airflow and pressure drop through this valve. This can be done by means of a device translating a suction signal into positioning of the airvalve, for instance by means ofa diaphragm.

It is however also possible to accomplish a nearly linear airvalve created suction curve by means of springloaded valves or hinged flapper valves. Four forms of execution shall be described here-after. These valves are designed to replace the laminar flow matrix, for instance the matrix 6 in FIG. 6.

FIG. 9 shows a simple springloaded plate valve taking the place of the matrix in the new primary stage carburetor similar to that of FIG. 6. This device creates the pressure drop AP in the air duct 32-33 by means of the spring 31. The tension of this spring rises proportional to the valve opening, starting with ZERO tension when the valve is just closed. Zero tension for the closed position means NO BIAS spring load.

FIG. 10 shows the suction-airflow relation obtained with such a valve and spring load. This curve is compared with aventuri curve and a laminar flow curve. It can be seen that the springloaded valve curve raises the low-end suction even more than a laminar flow matrix.

The total stroke for this valve is short. Therefore the spring rate has to be steep, and the spring has to be manufactured and positioned to very close tolerances.

FIG. 11 shows another design of an airvalve which approaches the linear pressure drop airflow relation of a matrix.

This airvalve consists again of an air duct 35-36, a floating valve 37 and a tension spring 38 of linear characteristic, which is attached to the air duct by means of the rod 39. This spring is of a much lower spring rate then that of FIG. 9, since the valve stroke is larger.

In the closed position of the valve 37 (dashed lines), the spring exerts again zero tension (no bias load). Under the influence of an airflow, the valve moves down and assumes a balanced position where the opening between the valve and the conical portion of duct 40 creates an airspeed, and therewith pressure drop, balancing the spring-tension for this particular valve opening.

The resulting pressure-drop airflow-relation is similar to that shown in FIG. 10 (for a straight conical section 40). The low rate spring is easier to manufacture to close tolerances than that of FIG. 9. Also the condition of zero bias load in the closed position is easier to maintain.

A further advantage of the design of FIG. 11 is its complete lack of friction, an extremely important feature for a mechanical device designed to replace the laminar flow matrix.

As explained before, and as FIG. 10 shows, the suction-airflow relation of this device creates even higher suctions at low airflows than the linear matrix. If this valve replaces the matrix 6 of FIG. 6, its higher suction generation at low airflows will create steeper transient curves i,j and k. In order to reduce the slope of these curves, the equivalent procedure as described in chapter 6b has to be used; it has been explained there that a shorter matrix, creating a smaller linear component of the total metering suction, is used, and the venturi throat narrowed down to a value where the venturi replaces the metering suction lost through the shortening of the matrix. Thus the total metering suction is maintained, but the linear component and consequently the amount of low speed enrichment reduced.

The equivalent procedure for the device of FIG. 9 and l 1 is to reduce the springrate and again replace the therewith reduced metering suction by means of a smaller venturi throat.

The foregoing shows that a special air valve, replacing the laminar flow matrix, does NOT have to duplicate a linear flow relation very closely. The devices of FIG. 9 and 11 are actually overdoing the ef-' fect of laminar flow matrix, with a relation approximating the equation Ap C.F.M.' they increase the low airflow enrichment even stronger then a pure linear Matrix. Yet, these devices are perfectly suited to produce transient curves which are close to the curves ij and k of FIG. 7. This is done by the simple expedient of reducing the airvalve-produced percentage of the total metering suction generation of the airvalve-venturi combination.

The criterion for the design of an airvalve simulating the effect ofa matrix is simply a relation of Ap C.F.M. 0.6 1.9. As long as the exponent is less than the two exponent of a purely turbulent venturi, some low airflow enrichment is obtained. This is the same condition as explained in chapter 66, Selection of Laminar Flow Matrix, except that the airvalve can create a relation with an exponent smaller then ONE, something which a laminar flow matrix can not accomplish, but which, as explained before, is usable for an accordingly selected airvalve venturi combination.

Consequently, the described airvalve indeed simulates the laminar flow matrix, AS USED in the new carburetor, namely in combination with a venturi.

In some cases it may, however be preferable, to simulate the straight line relation of a low Reynold number matrix more closely. FIG. 12 shows how this can be accomplished with a device almost identical to that of FIG. 11. The only difference is that the wall portion 41 of FIG. 12 is curved, rather then conical as in FIG. 11.

The curvature of the portion 41, in which the valve moves, determines the pressure drop-airflow relation. In the previously described device of FIG. 9, the flow area was (closely) proportional to the valve travel and therewith the tension of the (linear) spring. With the device FIG. 12, however, the throttling gap between the valve and the wall 41 depends on the profile of this wall. By means of the selection of this profile, any desired transient fuel-air ratio curve can be generated. The profile shown in FIG. 12 is designed to give an almost straight line relation between suction and airflow.

An improvement of the Matrix suction simulating device of FIG. 11 is shown in FIG. 13. This device takes over the function of BOTH the matrix and venturi.

FIG. 13 shows schematically a complete primary carburetor. generating the same mixture curves as shown in the curves ofFlG. 7.

The carburetor air inlet 50 connects to the venturi throat 53. The main throttle 55 controls the mixture flow to the carburetor outlet 52. The reset device consists again of the bypass throttle 68, the throttle shaft 69, the lever 60 attached to this shaft, and the roller 61 attached to the free end of this lever. Roller 61 is pulled by spring 63 against the face of the cam 62, which is rotated by the main throttle shaft 54.

The function of this reset device is the same as with FIG. 6. It discharges the reset air into the circular duct 67, where itjoins the mixture coming from the Venturi 53.

The combination of the laminar flow matrix simulating valve and the venturi is accomplished by means of the floating valve 56. As a valve it functions similar to the device of FIG. 11; it is suspended on a linear spring 59 which attaches by means of the rod 60 to the carburetor inlet wall 50.

Again, the springtension must be zero in the position of smallest flow area and increases in a linear function up to the stretch which creates the maximum intended pressure drop at the maximum downtravel of the valve 56. I

Contrary to the device of FIG. 11, the valve of FIG. 12 is streamlined, thus affording the great advantage of suction recovery.

In the previous device of FIG. 11 the valve only replaces the matrix of FIG. 6. There, the fuel discharge takes place downstream of this valve. A streamlined recovery with this design is impossible, since it would eliminate (recover) the very metering suction this valve is designed to create. The problem of a solution to the contradictory requirement of needing the valvecreated suction and advantage of suction recovery is solved with the device of FIG. 12.

' Here the fuel is discharged through the metering orifice 71, into an airbleed flow admitted at the bleed orifree 57. The resulting foam is discharged at the valve periphery, that is the points of highest suction, through radial holes 58.

The orifice 71 receives the fuel from a conventional float mechanism (not shown) which connects to the nipple 70. This stationary nipple connects by means of the highly flexible hose 72 to the metering orifice 71.

It can be seen that the fuel foam discharge travels with the downwards moving valve, always discharging at the narrowest ring area formed for each valve position, thus sensing the highest metering suction created by the valve and by the flared-out valve seat 51, for each valve position. The figure illustrates how the valve,.and valve seat 51 combine to form a venturi recovery.

To summarize: In FIG. 13, the function of the laminar flow matrix is simulated by the valve 58, its spring 59 and its profiled valve seat 51. At the same time, the venturi portion of the metering suction is created in the same device, by means of the streamlined valve 56 and the venturi 5351. This device gives the advantage of simplicity and suction recovery. The suction recovery, of course, extends the operating range of this primary stage carburetor.

It was previously explained that the springs for the valves of FIG. 9, 11, 12 and 13 have to give zero tension in the closed position, in order to create the matrix suction curve simulation.

This requirement can however be modified to avery slight degree, by giving this valve a constant bias" tension, in its closed position. This tension should be just enough to help to create the needed rich idle mixture. For a single orifice primary stage carburetor, this bias should normally be in the order of only 1 inch water. This bias-tension can be made changeable, for adjusting the idle mixture strength.

Still another springloaded airvalve design is shown in FIG. 14. This valve, is also designed to replace the laminar flow matrix 6 of FIG. 6.

The valve is formed by a leafspring 83, which, in its relaxed position, blanks off almost the entire airinlet to the valve body 80. This leafspring-valve 83 is attached to the body by means of screws 84.

As the airflow increases, the leafspring is deflected towards an open position. The spring rate changes during this opening movement, by developing the leaf spring over the profile 81 of the valve body. The selection of this profile makes it possible to vary the airflowpressure drop relation.

A further help in the selection of this curve is given by the profile of the wall 82. Just as in the case of the 

1. A two stage carburetor for an internal combustion engine having a primary carburetor section and a secondary carburetor section, at least said primary carburetor section comprising a. a throttle body containing at least one main induction passage, b. at least one main throttle arranged in said main induction passage for controlling the flow of combustible mixtures from said induction passage and into said engine, c. at least one fuel level holding device, d. means for producing a fuel metering vacuum, e. at least one fuel metering orifice effective for receiving fuel from said fuel level holding device and being subjected to said fuel metering vacuum, f. said means for producing a fuel metering vacuum comprising first vacuum generating means for developing a first vacuum of variable value in the vicinity of said fuel metering orifice dependent upon the rate of air flow through said main induction passage, second vacuum generating means for developing a second vacuum of variable value in the said vicinity of said fuel metering orifice dependent upon the rate of air flow through said main induction passage, the value of said first vacuum of variable value varying at a rate different from the rate at which said second vacuum of variable value varies with respect to said rate of air flow through said main induction passage, said first and second vacuums effectively combining in said vicinity to result in a pneumatic summation thereof to define said fuel metering vacuum also of a variable value, said fuel metering vacuum having a relationship to the rate of air flow through said main induction passage expressed by the equation Delta P varies as C.F.M.x wherein:
 1. Delta P represents the pressure differential created by said fuel metering vacuum
 2. A carburetor for an internal combustion engine, comprising a. at least one throttle body containing at least one first passage means for the formation and conduction of an excessively rich fuel-air mixture, b. at least one throttle means arranged in said first passage means for controlling the flow of said mixture therepast, c. at least one fuel level holding device, d. first means situated in said first passage means for producing a fuel-metering pressure differential, e. at least one fuel metering orifice effective for receiving fuel from said fuel level holding device and being subjected to said fuel-metering pressure differential for producing said excessively rich fuel-air mixture, f. an additional large throttle body containing a main passage, g. an air throttle arranged in said main passage, h. a venturi arranged in said main passage downstream of said air throttle, i. said first passage means being arranged for discharging said excessively rich fuel-air mixture into said venturi arranged in said main passage, j. said first means situated in said first passage means comprising first vacuum generating means for developing a first vacuum of variable value in the vicinity of said fuel metering orifice dependent upon the rate of air flow through said first passage means, second vacuum generating means for developing a second vacuum of variable value in the said vicinity of said fuel metering orifice dependent upon the rate of air flow through said first passage means, the value of said first vacuum of variable value varying at a rate different from the rate at which said second vacuum of variable value varies with respect to said rate of air flow through said first passage means, said first and second vacuums effectively combining in said vicinity to result in a pneumatic summation thereof to define said fuel-metering pressure differential also of a variable value, said fuel-metering pressure differential having a relationship to the rate of air flow through said first passage means expressed by the equation Delta P varies as C.F.M.x wherein:
 2. C.F.M. represents the cubic feet of air flow per minute and
 3. the exponent X has a value greater than 1.2 but less than 1.9, thereby creating a fuel-air ratio cUrve of said combustible mixture which becomes richer in fuel with reduced airflow, g. at least one reset device comprising means to vary the said fuel-air ratio and comprising a scheduling mechanism which couples said means to vary the fuel-air ratio to said main throttle, said mechanism scheduling the magnitude of fuel-air ratio variations in dependence of opening positions of the main throttle, said scheduling mechanism being calibrated to correct said fuel-air ratio, which becomes richer with reduced airflow, to the desired roadload curve, h. the secondary carburetor comprising a secondary main throttle, and a scheduling mechanism which couples said means to vary the fuel-air ratio of the primary carburetor to said secondary main throttle, said mechanism scheduling the magnitude of fuel-air ratio variations of said primary carburetor in dependence of opening positions of said secondary main throttle, said scheduling mechanism being calibrated to correct the fuel-air ratio of said primary carburetor to compensate for fuel-air ration aberrations of the secondary carburetor.
 2. C.F.M. represents the cubic feet of air flow per minute and
 2. C.F.M. represents the cubic feet of air flow per minute and
 3. The carburetor of claim 2 with two excessively rich carburetors working progressively in the manner of two stage carburetors.
 3. the exponent X has a value greater than 1.2 but less than 1.9, thereby creating a fuel-air ratio cUrve of said combustible mixture which becomes richer in fuel with reduced airflow, g. at least one reset device comprising means to vary the said fuel-air ratio and comprising a scheduling mechanism which couples said means to vary the fuel-air ratio to said main throttle, said mechanism scheduling the magnitude of fuel-air ratio variations in dependence of opening positions of the main throttle, said scheduling mechanism being calibrated to correct said fuel-air ratio, which becomes richer with reduced airflow, to the desired roadload curve, h. the secondary carburetor comprising a secondary main throttle, and a scheduling mechanism which couples said means to vary the fuel-air ratio of the primary carburetor to said secondary main throttle, said mechanism scheduling the magnitude of fuel-air ratio variations of said primary carburetor in dependence of opening positions of said secondary main throttle, said scheduling mechanism being calibrated to correct the fuel-air ratio of said primary carburetor to compensate for fuel-air ration aberrations of the secondary carburetor.
 3. The exponent X has a value greater than 1.2 but less than 1.9, thereby creating a fuel-air ratio curve for said mixture which becomes richer in fuel with reduced airflow, k. and a scheduling mechanism operatively coupling said air throttle to said mixture-controlling throttle means so as to cause said air throttle to function as a reset device whereby changes in the fuel-air ratio of said mixture are affected by opening of said air throttle, said mechanism scheduling the magnitude of said fuel-air ratio changes caused by said air throttle in dependence of opening positions of the said mixture-conTrolling throttle means, said scheduling mechanism being calibrated to correct said excessively rich fuel-air ratio, which becomes richer with reduced airflow, to the desired roadload curve.
 4. A carburetor for an internal combustion engine, comprising a throttle body, a main induction passage formed therethrough, at least one throttle valve situated in said induction passage for movement relative thereto in order to thereby variably control the flow of a fuel-air mixture through said induction passage, a venturi in said induction passage upstream of said throttle valve, first air bleed means including a bleed air chamber, first conduit means communicating between said air bleed chamber and said induction passage at said venturi, fuel supply conduit means including fuel metering orifice means communicating between a related source of fuel and said bleed air chamber, air passage means communicating between a related source of substantially ambient atmospheric air and said bleed air chamber, means situated in said air passage means defining a laminar flow matrix means, said laminar flow matrix means being effective to produce a vacuum in said bleed air chamber in response to air flow through said venturi in order to thereby determine the rate of flow of said fuel from said fuel supply conduit means into said bleed air chamber and through said first conduit means into said induction passage, said laminar flow matrix means being effective to provide a restrictive effect to the flow of said air through said air passage means sufficient to cause the fuel-air ratio curves for variable engine R.P.M. at constant throttle positions to be displaced towards richer fuel-air ratio values at the low R.P.M. end of said curves if compared to fuel-air ratio curves recorded with the same carburetor but without said laminar flow matrix means being installed in said air passage means, and at least one reset means effective for varying the fuel-air ratio of the fuel and air flowing through said induction passage, said reset means comprising scheduling means operatively coupling said reset means to said throttle valve in order to thereby cause said reset means to be actuated in response to opening and closing movement of said throttle valve, said scheduling means being effective for variably and in accordance with the position of said throttle valve reducing the effect of said laminar flow matrix means in determining the value of the fuel-air ratio curves at constant engine R.P.M.
 5. The carburetor of claim 4 in which said reset means comprises a bypass air throttle and said scheduling means comprises a lever and cam device operatively connecting said throttle valve with said bypass air throttle.
 6. The carburetor of claim 4 in which said reset means comprises an airvalve and said scheduling means comprises a lever and cam device operatively connecting said throttle valve with said airvalve for actuation of said airvalve in response to movement of said throttle valve.
 7. The carburetor of claim 4 in which said reset means comprises an interior discharge throttle, and said scheduling means comprises a lever and cam device operatively connecting said throttle valve with said interior discharge throttle for actuation of said interior discharge throttle in response to movement of said throttle valve.
 8. The carburetor of claim 4 in which said reset means comprises a port in said air passage means connecting ambient air to said bleed air chamber, and a plate valve generally controlling the effective area of said port, said plate valve being operatively coupled to said throttle valve, and said scheduling means comprising contoured slot means formed through said plate valve as to be in general registry with said air passage means.
 9. A carburetor for an internal combustion engine, comprising a throttle body, a main induction passage formed therethrough, at least one throttle valve situated in said induction passage for movement relative thereto in order to thereby variably control the flow of a fuel-air mixture through said induction passage, a venturi in said induction passage upstream of said throttle valve, a fuel reservoir including vent means, fuel delivery passage means including fuel metering restriction means communicating between said fuel reservoir and said venturi, air passage means communicating between a first conduit portion leading to said induction passage and inlet orifice means leading to ambient atmosphere, means situated in said air passage means defining a laminar flow matrix means, a second conduit portion communicating between said vent means and said air passage means at a point downstream of said inlet orifice means but upstream of said laminar flow matrix means, said inlet orifice means and said laminar flow matrix means being effective to alter the magnitude of vacuum in said induction passage in the vicinity of said first conduit portion in order to thereby cause the fuel-air ratio curves for variable engine R.P.M. at constant throttle valve positions to be displaced towards richer fuel-air ratio values at the low R.P.M. end of said curves if compared to fuel-air ratio curves recorded with the same carburetor but without said laminar flow matrix means being installed in said air passage means, and at least one reset means effective for varying the fuel-air ratio of the fuel and air flowing through said induction passage, said reset means comprising scheduling means operatively coupling said reset means to said throttle valve in order to thereby cause said reset means to be actuated in response to opening and closing movement of said throttle valve, said scheduling means being effective for variably and in accordance with the position of said throttle valve reducing the effect of said laminar flow matrix means in determining the value of the fuel-air ratio curves at constant engine R.P.M.
 10. The carburetor of claim 9 in which said reset means comprises a bypass air throttle and said scheduling means comprises a lever and cam device operatively connecting said throttle valve with said bypass air throttle.
 11. The carburetor of claim 9 in which said reset means comprises an airvalve and said scheduling means comprises a lever and cam device operatively connecting said throttle valve with said airvalve.
 12. The carburetor of claim 9 in which said reset means comprises an interior discharge throttle and said scheduling means comprises a lever and cam device operatively connecting said throttle valve with said interior discharge throttle.
 13. The carburetor of claim 9 in which said reset means comprises a plate valve controlling said inlet orifice means, said plate valve being operatively coupled to said throttle valve, and said scheduling means comprising contoured slot means formed generally through said plate valve and in general registry with said inlet orifice means.
 14. A carburetor for an internal combustion engine, comprising a carburetor body, induction passage means formed through said body for communicating between a source of air and an intake of said engine, variably positionable and openable throttle valve means situated within said induction passage means for controlling the flow of air and fuel through said induction passage means and into said intake of said engine, a source of fuel, fuel discharge means communicating with said source of fuel and situated as to discharge metered fuel flow into said induction passage means at a point upstream of said throttle valve means, first vacuum generating means for developing a first vacuum of variable value in the vicinity of said fuel discharge means dependent upon the rate of air flow through said induction passage means, second vacuum generating means for developing a second vacuum of variable value in the said vicinity of said fuel discharge means dependent upon the rate of air flow through saId induction passage means, the value of said first vacuum of variable value varying at a rate different from the rate at which said second vacuum of variable value varies with respect to said rate of air flow through said induction passage means, said first and second vacuums effectively combining in said vicinity to result in a pneumatic summation thereof to define a metering vacuum of variable value in said vicinity causing the rate of flow of said metered fuel flow to be dependent upon the value of said metering vacuum, and additional means responsive to demands for increased power from said engine for at least temporarily increasing the value of said metering vacuum.
 15. A carburetor according to claim 14, wherein said additional means is operatively connected to said throttle valve means.
 16. A carburetor according to claim 14, wherein said first vacuum generating means comprises a venturi formed in said induction passage means.
 17. A carburetor according to claim 14, wherein said first vacuum generating means comprises a venturi formed in said induction passage means, and wherein said second vacuum generating means comprises air-flow restriction means having a characteristic of producing a flow of air therethrough generally proportional to the pressure differential across said restriction means.
 18. A carburetor according to claim 14, wherein said fuel discharge means comprises first fuel discharge port means opening at one end into said induction passage means, a chamber formed upstream of said discharge port and in communication with the other end of said fuel discharge port, fuel delivery conduit means communicating between said source of fuel and said chamber, air passage means communicating between a source of air and said chamber, and wherein said second vacuum generating means is situted within said air passage means.
 19. A carburetor according to claim 14, wherein said additional means comprises variably openable air bleed means effective for admitting bleed air into said induction passage means, said air bleed means being moved toward a more nearly closed position in response to said demands for increased power from said engine.
 20. A carburetor according to claim 19, wherein said bleed air is admitted into said induction passage means generally at a point upstream of said throttle valve means.
 21. A carburetor according to claim 14, wherein said second vacuum generating means comprises air-flow restriction means having a characteristic of producing a flow of air therethrough generally proportional to the pressure differential across said restriction means.
 22. A carburetor according to claim 21, wherein said restriction means comprises a matrix of laminar flow conduit portions.
 23. A carburetor according to claim 14, wherein said additional means comprises a bleed air passage communicating generally between a source of air and said induction passage means. A variably positionable air valve for controlling the rate of flow of air through said bleed air passage, and linkage means operatively interconnecting said throttle valve means and said air valve.
 24. A carburetor according to claim 23, wherein said bleed air passage communicates generally between a source of air and said induction passage means at a point generally above said throttle valve means.
 25. A carburetor according to claim 23, wherein said linkage means comprises cam means contoured as to generally cause said air valve to further restrict the flow of said bleed air through said bleed air passage means as said throttle valve means is moved from an idle position to a more nearly wide open position. 